Electric valve control system



g- 5, 1941- s. R. DURAND 2,251,484

7 ELECTRIC VALVE CONTROL-SYSTEM Filed Sept. 30, 1939 Y/MO/WWE Patented Aug. 5, 1941 ELECTRIC VALVE CONTROL SYSTEM Samuel R. Durand, Milwaukee, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application September 30, 1939, Serial No. 297,219

23 Claims.

This invention relates in general to electric valve control systems and more particularly to means for controlling the ignition and excitation of a group of electric valves of the single anode mercury cathode type forming part of an electric current converting system.

Electric current converting systems frequently comprise a transformer associated with a group of electric valves provided with anodes and with a mercury cathode arranged within a common casing. The valves are then rendered and maintained conductive by a single set of ignition and excitation apparatus associated with the common cathode. When the valves are provided with separate cathodes which are severally to be rendered and maintained conductive, each cathode is provided with a separate ignition and excitation system. The different cathodes should then be rendered simultaneousl conductive to prevent the flow of dissymmetrical currents therethrough which would cause saturation of the converter transformer traversed by such currents. In the event that excitation current fails in one of the valves the excitation should be reestablished therein within the shortest possible time. Until the current through such valve can be reestablished however the particular valve connected to the opposite phase of the transformer or other alternating current network associated With the valves is preferably rendered non-conductive to prevent the flow of dissymmetrical currents through the network. The remainder of the valves re however preferably maintained conductive to insure uninterrupted transmisison of energy through the system. If the defective valve cannot be rendered conductive Within a predetermined time interval the entire converting system should be operatively disconnected from the associated circuits.

It is therefore one of the objects of the present invention to provide an electric valve control system for a plurality of cooperating electric valves by means of which the different valves may be simultaneously rendered conductive.

Another object of the present invention is to provide an electric valve control system for a plurality of cooperating electric valves by means of which a valve may be rendered nonconductive while the valve connected to the opposite phase of the system is without excitation current.

Another object of the present invention is to provide an electric valve control system for a plurality of cooperating electric valves by means of which all the valves of the system may be disconnected from the associated circuits when one or more of the valves cannot be rendered conductive within a predetermined time interval.

Another object of .the present invention is to provide an electric valve control system for a plurality of cooperating electric valves by means of which some of the valves may be maintained in normal operation while another of the valves is momentarily inoperative.

Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, which diagrammatically illustrates one embodiment of the present invention applied to the control of a group of six valves forming part of an alternating current rectifying or direct current inverting system.

Referring more particularly to the drawing by characters of reference, reference numeral 6 designates a polyphase alternating current circuit to be connected with a direct current circuit 1 through a converting system comprising a transformer 8 and a plurality of interconnected electric valves 9 to I4 inclusive. or circuit 7 may be chosen as supply circuit for the system but it will be assumed that circuit 6, for example, is the supply circuit energized from a suitable generator (not shown) and that circuit 1 is the output circuit transmitting current to suitable load devices (not shown). Transformer 8 comprises a primary winding I 5 subdivided into' a plurality of phase portions connectable with circuit 6 through a switch 11 serving to control the connection between circuits 6 and 7 through the valves. Winding I6 is inductively related with a secondary winding l8 constituting anetwork divided into a plurality of pairs of opposite phase portions. The different pairs of phase portions of winding I8 are severally connected with one of the conductors of circuit 1 through pairs of valves such as valves 9, l2. Winding I3 is preferably arranged to define a plurality of neutral points severally connected with the other conductor of circuit 7 through an interphase transformer l9.

Valves 9 to M are preferably of a uniform design and each comprise a casing which may be made of insulating or of conductive material. If the different valve casings are conductive, as will be assumed hereinafter, they maybe either insulated from each other or else maintained at a common potential by a conductive connection therebetween as at 25. Valve 9 comprises a cathode 29 consisting of apool of a suitable liquid conductor such as mercury which is preferably insulated from the associated casing 2|. Valve 9 further'comprises a single main anode 22 cooperating with cathode 20 for the flow of current between circuits 6 and 1 connected therewith.

Valve 9 may be rendered conductive by an ignition system comprising an ignition anode 23 arranged adjacent the surface of cathode 20 and connected with casing 2| through a resister 24. Ignition current may be supplied to anode 23 from circuit 6 through auxiliary cir- Either circuit 6' cuits comprising the usual step down transformer 25, the contacts of a control switch or contactor 21, contacts Era of an adjustable time delay lockout relay 23, contacts 2% of an auxiliary relay 29, an ignition transformer so, a current rectifying device 3i, contacts 32d of an excitation relay 32, a resistor 33, casing 2i and resistor 24. The ignition current returns to rectifier 3| through cathode 2%, the positive conductor of circuit 1 and a smoothing reactor 3%.

Momentary engagement of anode 23 with cathode 213 to establish a cathode spot rendering the cathode conductive is controlled by means of a solenoid 35 which may be energized from circuit 5 through transformer 2%, switch 21, contacts 31d of a control relay 31, and contacts die of relay T22. Solenoid 35 may cause engagement of ignition anode 23 with cathode 2% in any known manner, for example by attracting an armature forming a piston projecting a jet of cathode material against anode 23. Valve 9 is provided with excitation anodes 38 connected with circuit 9 through transformer 26, switch 21, a bank of reactors 15, a transformer 39, the coils of relay 32, and a pair of resistors It. The excitation current supplied to cathode through anodes 33 returns to transformer 39 through one of a group of reactors M.

It has been found that to obtain a stable excitation arc the electrical characteristics of the o excitation circuits cannot be chosen arbitrarily and need to be determined experimentally. For example, it has been found that a satisfactory excitation circuit for a group of six valves delivering current up to 2000 amperes at 600 volts may comprise the following elements: reactors Q5 of 20 millihenries each, transformer for 230 volts primary voltage, '12 volts secondary voltage, res'istors ii) of 5 ohms each, and reactors M of 30 millihenries each. Each excitation arc then carries a current of approximately 5 amperes (60 cycle supply).

The conductivity of valve 9 for the flow of current between anode 22 and cathode 25 may be controlled by means of a control grid 32'. Valve 9 may be rendered and maintained non-conductive by impressing on grid 2 a negative potential from a suitable source of direct current such as a generator 43 through a voltage divider M, contacts 4-50 of an excitation relay 36 associated with valve I2, and a grid resistor 41. Generator 43 may be driven by any suitable means such as a motor 48 energized from circuit 6 through transformer 25. Valve 9 may be rendered conductive and its conductivity may be varied by impressing on grid 42 an adjustable unidirectional potential obtained from a second voltage divider 49 connected with generator 43 and a suitable alternating potential from a transformer 56 energized from transformer 25. The connection between transformer 50 and grid t2 may include contacts 46b of relay 45.

Valves It to I4 inclusive are provided with electrodes similar to those of valve 9 and connected in a similar manner. In particular valve I2 is provided with a main anode 5I, a cathode 52 and a control grid 53. The cathodes of the different valves are directly connected with one of theconductors of circuit 1 and are therefore at a common potential different from the potential of the casings. The solenoids controlling the ignition of the different valves may be simultaneously'connected with circuit 5 and may likewise simultaneously be disconnected from circuit 6 by means of contacts 31a of relay 31 for causing simultaneous initiation of the flow of current through the different valves. To supply the necessary current impulses to the solenoids relay 31 is alternately energized and deenergized during predetermined time intervals by suitable timing means preferably comprise a timing relay 54 for connecting the coil of relay 31 with circuit 6 through contacts 54a and 29b. The coil of relay 54 is energized from circuit 6 through rectifier 3I contacts 311) of relay 31 and contacts 56a of a second timing relay 56. The coil of relay is energized from circuit 6 through rectifier 3| and through contacts 310 of relay 31. In order to permit a convenient adjustment of the times of operation of relays 54 and 56, these relays are pref erably chosen of the well known flux decay type in which release of the armature is controlled by the decay of the flow of current through an adjustable short circuited conductor.

As a result of these connections, relay 54 is operable responsive to energization of relay 31 to deenergize relay 31 after a predetermined time interval and relay 58 is operable responsive to deenergization of relay 31 to reenergize relay 31 after another predetermined time interval. Current impulses are thereby caused to be impressed from circuit 6 on the different ignition solenoids through contacts 31a. The coil of relay 29 controlling the operation of relay 31 is connected with circuit 6 through contacts such as 32a, 46a of the different excitation relays associated with valves 9 to Hi respectively to cause relay 29 to disconnect the solenoids from the current impulse supplying relay 31 in response to the flow of current simultaneously through all of the valves. Contacts 28a are connected in series with contacts 2% to render the ignition and excitation system inoperative after a predetermined time interval following initiation of the operation of the ignition system by closure of switch 21. Switch 21 is provided with an operating coil which may be energized from circuit 6 through transformer 26, a normally open push button switch 51, the contacts of relays 58 energized from circuit 6 through current transformers 59 and through a normally closed push button switch 60. A holding circuit for the coil of relay 21 is provided in parallel with switch 51 through one of the main contacts of relay 21 and through contacts 28a. Push button switch 50 also controls the energization of coil I1a for holding the latch I1b of switch I1 in engaged position. Although the system may be so arranged that switch I1 may be closed before initiating the ignition operation of the valves, it is preferable to interlock switch I1 with the ignition system of the valves to permit closure of the switch only when all the valves have become conductive. For this purpose the closing coil I10 of switch I1 is connected with circuit 6 through contacts 290 of switch 29 and through a normally open push button switch BI. Switch I1 may be caused to open upon opening of switch 21 by means of a trip coil I1d connected with circuit 6 through contacts We of switch I1 and through auxiliary contacts 21a of switch 21.

The system being connected as shown on the drawing and circuit 6 being energized, the system may be put in operation by momentarily closing switch 51. Current then flows from transformer 26 through switch 51, the coil of switch 21, the contacts of relays 58 and switch 60 back to transformer 25. Switcl'l21 closes and completes the holding circuit for the coil thereof across switch 51. The coil of relay 28 is also energized through contacts 29a but the relay opens contacts 28a thereof only if it remains energized during a relatively long time interval. Current also flows from transformer 26 through switch 21, contacts 28a, contacts 2% and the primary winding of transformer 36 to induce current through the secondary winding of transformer 3!], rectifier 3|, contacts 31b, the coil of relay 54 and contacts 56a back to rectifier 3|. Relay 54 immediately closes contacts 5 5a. Another circuit is thereby completed between transformer 26 and the coil of relay 3'! through switch 21, contacts 28a, 29b, and 56a. Relay 3'! operates, deenergizing the coil of relay 54 by opening contacts 311) and also energizing the coil of relay 55 through contacts 310. Relay 55 opens contacts 55a which cooperate with contacts 3'lb in deenergizing relay 54. After a predetermined time interval relay 54 opens contacts 54a to deenergize relay 31. Relay 3! returns to the position shown and deenergizes relay 56. After another predetermined time interval relay 55 recloses contacts 58a and the above sequence of operation of relays 3?, 54 and 56 is immediately restarted. Such operation is continually repeated until interrupted by operation of relay 29 or of relay 28. Relay 37 is thus continually energized during time intervals of predetermined duration separated by other time intervals of another predetermined duration.

When relay 3? is energized all the solenoids of valves 9 to M are simultaneously energized through contacts 31a and through contacts of the associated excitation relays such as contacts 32c, 656. If the solenoids are provided with pistons immersed in the cathodes, the pistons are simultaneously attracted to cause the cathode 5:;

jets to impinge simultaneously against the associated ignition anodes. Parallel ignition circuits for the different valves are then completed from rectifier 3! such as the circuit associated with valve 9 and comprising contacts 32d, ignition resistor 33, the casing of valve 9, resistor 24, ignition anode 2-3, cathode 28, and reactor 34 back to rectifier 3.4. When relay 31 is deenergized the solenoids are simultaneously disconnected from circuit 5 to cause interruption of the jets of cathode material. Relays 31, 54 and 55 are so adjusted that the solenoids are energized during time intervals which are sufficiently long to cause the jets to impinge on the ignition anodes but which are also sufficiently short to prevent impact of the pistons against the cooperating cylinders at the end of their stroke. The relays should also deenergize the solenoids during a sufiiciently long time interval to permit return of the pistons to the initial positions thereof.

Vifhen the interrupted jets fall back into the corresponding cathodes, arcs are simultaneously drawn between the ignition anodes and the oathodes of all the valves, thereby establishing cathode spots rendering the cathodes simultaneously conductive. If for any reason however any one of the cathodes fails to carry current the associated solenoid continues to receive current impulses through contacts 3'ia of relay 3'! to repeat the ignition operation until the cathode is rendered conductive.

Vfhen cathode 2%), for example, has been rendered conductive, alternate half Waves of current flow from transformer 39 through the coils of relay 32, resistors 43, excitation anodes 38, cathode 2i] and one of reactors 4! back to transformer 39. The excitation current impulses are caused to overlap by the inductance of reactors 4| and 45 so asto supply to cathode 25 an excitation 75 current without discontinuity. Thefiow of excitation current through valve 9 and through the coils of relay 32 causes the relay to disconnect solenoid from relay 3! and to disconnect ignition anode 23 from rectifier 3|. If all the valves have become conductive and are carrying excitation current before relay 23 opens contacts 28a, all the excitation relays operate and complete a circuit for the coil of relay 29 through the contacts such as 32a, a of the excitation relays. Relay 29 is thereby energized and opens contact 291), thus cooperating with the excitation relays in disconnecting the ignition anodes and other ignition apparatus from circuit 5 in response to the flow of current simultaneously through all the valves.

Relay 29 deenergizes relay 28, which therefore leaves contacts 28a closed. Relay 2% also closes contacts 290, thereby permitting switch i! to be closed by connecting solenoid i'lc with transformer 25 through switch 6!. Switch l l is thereafter maintained closed by means of latch I'll), which is maintained in latching position by coil Ila energized from the transformer 26 through switch and through the contacts of relays 58. Valves 9 to M then transmit current from circuit 6 to circuit 1 in the well known usual manner under the control of the grids, which are then energized from voltage divider 49 and trans former 563 through the contacts such as 32b, 45b of the excitation relays. The flow of current through valve 9, for example, may take place when anode 22 is at a potential which is more positive than the potential of all other anodes, and is initiated upon grid 42 reaching substantially a positive potential with respect to the potential of cathode 25. The different valves carry current in sequence and the different valve current impulses combine into a substantially uniform flow of current delivered to circuit 1. During the idle periods of the valves the cathodes thereof continue to carry excitation current and are therefore maintained continuously conductive. The conductivity of the cathodes therefore does not need to be restored at the inception of each operating period of the valves. The above described operation is the normal operation of the system. Several abnormal operating conditions thereof will be considered hereinafter.

Itmay happen that an ignition arc cannot be struck in one of valves 9 to M for any reason such as excessive gas pressure therein. Assuming for example that cathode 25 remains nonconductive after several operaticnsof solenoid 35, relay 32 remains in the position shown and even if the other excitation relays have functioned relay 29 remains in the position shown. Relays 31, 54 and 56 accordingly continue to supply current impulses to solenoid 38. After a predetermined time interval relay 28 opens contacts 28a, thereby interrupting the holding circuit for the coil of switch 21. The setting of relay 28 is such that the time interval is of suficient length to permit relays 3'1, 54 and 56 to operate the desired number of times. This number of operations may be any suitable number, such as twelve for example, insuring the certain success of the ignition operation if the valve is in its normal operating condition. Operation of relay 23 causes switch 2'! to return to the position shown and the entire system is rendered inoperative. The cause of trouble may then be investigated and further attempts may be made to start the system by reclosing push button switch 5?.

. During normal operation of the system the fiow of excitation current through one of the valves may fail for any reason such as abnormal pressure or temperature conditions of the valve and the valve becomes non-conductive for the flow of current between the anode and the oathode thereof. If the flow of excitation current fails through valve 9 for example current continues to flow through the other five valves. Half wave impulses of current flowing through valve 12 are then no longer associated with intervening half waves of current flowing through valve 9 connected to the opposite phase of winding l8, with the result that the current flowing through the associated phase portion of winding l6 becomes dissymmetrical. As is well known this occurrence causes the core of transformer 8 to gradually assume a unidirectional magnetic saturation and the flow of magnetizing current taken by transformer 8 from circuit 6 gradually assumes an excessive magnitude.

Before the flow of current through transformer 3 increases materially however relay 32 returns to the position shown, opening contacts 3% to disconnect grid 53 of valve l2 from transformer 59 and also closing contacts 32c connecting grid 53 with voltage divider 44. The taps of voltage divider 44 are so adjusted as to cause impression on grid 53 of a potential which is negative with respect to the cathode potential so as to prevent further flow of current through valve l2 although cathode 52 remains in conductive condition. Valves 9 and i2 are then both deprived of anode current and the flow of energy between circuits 6 and l continues through valves I0, ll, l3 and I4 only. The currents flowing through the different phase portions of transformer 8 are then unbalanced but they are no longer dissymmetrical so that the system may continue to function in this manner at least until the conductivity of valve 9 has been restored. Relay 32, having re turned to the position shown in response to the failure of the flow of current through valve 9, opens contacts 32a and causes relay 29 to return to the position shown. Relays 32 and 29 thus cooperate to connect ignition anode 23 with circuit B through rectifier iii, to render relays 31, 54 and 56 operative to convert current from circuit G into impulses, and to connect solenoid 3'6 with relay 3?. The ignition solenoids of the operating valves however remain disconnected from the ignition system by the associated excitation relays.

It will be observed that the ignition process is not affected by the number of valves being ignited even if the casings of the valves are conductively connected. The flow of current through any one of the ignition resistors such as 24 causes a voltage drop therein maintaining the valve casing and the other ignition anodes at such potential as to permit operation thereof. The flow of current from rectifier 31' through the casings and the ignition anodes is regulated by the resistors such as 33 to the proper value for the number of ignition anodes being utilized.

When relay 29 returns to the position shown, the coil of relay 28 is again energized through contacts 23a. If the conductivity of valve 9 is restored before relay 28 opens contacts 28a, relay 32 again operates to disconnect ignition anode 23 and solenoid 35 from the associated circuits. Relay 32 also restores the connection of grid 53 with transformer E! and the converting system is returned to its normal operating condition.

If however the renewed initiation of the current fiow through valve 9 cannot be obtained,

relay 28 is enabled to open contacts 28a after a predetermined time interval following initiation of the operation of relays 31, 54, and 55. The coil of switch 21 is thereby deenergized and switch '51 disconnects the ignition and excitation circuits of all the valves from circuit 8. The valves are thus deprived of excitation current and the fioW of current through the valves accordingly stops as soon as the last operating anode has become negative with respect to the associated cathode. The valves are thus rendered non-conductive by lack of excitation. The excitation relays such as 32 and 46 return to the position shown, thereby connecting all the control grids with voltage divider 44 through the contacts such as 320, 450 of the relays. The potentials of the grids are thereby modified from values permitting sequential flow of current through the valves to a value preventing such flow of current. Upon return of switch 21 to the position shown coil Fla is deprived of current while trip coil Hat is enerigized through contacts 21a. The trip coil withdraws latch llb to enable switch I! to open. The system is then returned to the condition shown on the drawing and the cause of failure of valve 9 to carry current may be investigated before attempts are made to restart the entire system.

Although but one embodiment of the invention has been illustrated and described it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the inven tion or from the scope of the appended claims. Some of the features of the invention disclosed herein are claimed in a copending application of Samuel R. Durand, Serial No. 394,991, filed May 24, 1941.

It is claimed and desired to secure by Letters Patent:

1. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation of current flows through the different said valves comprising means for connecting said solenoids with said source and for simultaneously disconnecting all said solenoids from said source.

2. In a control system for an electric valve comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of said ignition anode with said cathode, a source of current connected with said ignition anode and with said cathode, and means for supplying current impulses to said solenoid comprising a control relay for connecting said solenoid with said source and timing means connecting said relay with said source for causing alternate energization and deenergization of said relay during predetermined time intervals.

3. In a control system for an electric valve comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of said ignition anode with said cathode, a source of current connected with said ignition anode and with said cathode, and means for supplying current impulses to said solenoid comprising a control relay for connecting said solenoid with said source, a timing relay for connecting said control relay with said source and operable responsive to energization of said control relay to de energize said control relay after a predetermined time interval, and a second timing relay responsive to deenergization of said control relay for causing the first said timing relay to reencrgize said control relay after another predetermined time interval.

l. In a control system for a plurality of interconnected electric valves each comprising an ig nition anode, a cathode, and a solenoid for controlling the engagement of, the ignition anode with the associated cathode, a source of current connected with said ignition anodes and With said cathodes, and means for supplying current simultaneously to all said solenoids comprising a-control relay for connecting said solenoids with said source and timing means connecting said relay with said sour e for causing alternate energization and deenergization of said relay during predetermined time intervals.

5. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for supplying current simultaneously to all said solenoids comprising a control relay for connecting said solenoids with said source, a timing relay for connecting said control relay with said source and. operable responsive to energization of said control relay to deenergize said control relay after a predetermined time interval, and a second timing relay responsive to deenergization of said control relay for causing the first said timing relay to reenergize said control relay after another predetermined time interval.

6. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation of current flows through the difierent said valves comprising means for supplying simultaneous current impulses from said source to all said solenoids and means responsive to the flow of current simultaneously through all said valves for disconnecting all said solenoids from said current impulse supply means.

'7. In a. control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation of current flows through the difierent said valves comprising means for supplying simultaneous current impulses from said source to all said solenoids and means responsive to the flow of current simultaneously through all said valves for disconnecting said ignition anodes from said source.

8. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, andmeans for causing simultaneous initiation of current flows through the different said valves comprising means for supplying simultaneous current impulses from said source to all said solenoids and means responsive to the flow of current simultaneously through all said valves for disconnecting all said solenoids from said current impulse supply means and for disconnecting said ignition anodes from said source.

9. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for'controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation ,of current flows through the different said valves comprising means for supplying simultaneous current impulses from said source.

to all said solenoids and means associated with each said, valve each responsive to the flow of current through the associated valve for disconnecting the solenoid of said associated valve from said current impulse, supply means.

10. In a control system for a plurality of interconnected electric valves each comprising anignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation of current flows through the different said valves comprising means for supplying simultaneous current impulses from said source to all said solenoids and means associated with each said valve each responsive to the flow of current through the associated Valve for disconnecting the ignition anode of the associated valve from said source.

11. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means for causing simultaneous initiation of current flows through'the different said valves comprising means for supplying simultaneous current impulses from said source to all said solenoids and means associated with each said valve each responsive to the flow'of current through the associated valve for disconnecting the solenoid of the associated valve from said current impulse supply means and for disconnecting the ignition anode of the associated valve from said source.

12. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, means comprising a source of current connected with said cathodes operable responsive to failure of the flow of cur-- rent through any one of said valves to supply current impulses to the solenoid of said one of said valves only and to connect said source with the ignition anode of said one of said valves only.

13. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, and means forcausing simultaneous initiation of current flows through the difierent said valves comprising means for supplying recurring simultaneous current impulses from said source to all said solenoids and means responsive to initiation of the operation of the first said means for rendering the first said means inoperative after supply of a predetermined numher of successive impulses to any one of said solenoids.

14. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, means for supplying current impulses from said source to said solenoids, and means responsive to failure of the flow of current through any one of said valves for connecting the ignition anode of said one of said valves with said source and for connecting the solenoid of said one of said valves with the first said means.

15. In a control system for a plurality of inter connected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, a source of current connected with said ignition anodes and with said cathodes, means for converting current from said source into impulses, and means responsive to failure of the flow of current through any one of said valves for connecting the ignition anode of said one of said valves with said source, for rendering the first said means operative and for connecting the solenoid of said one of said valves with said source through the first said means.

16. In a control system for a plurality of electric valves each comprising a conductive casing, an ignition anode, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, the casings of the different said valves being at a common potential and the cathodes of the different said valves being at another common potential, a source of current connected with said cathodes and with said casings, a plurality of resistors each connecting one of said casings with the associated one of said ignition anodes, and means for supplying current impulses from said source to said solenoids.

17. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, a cathode, and a solenoid for controlling the engagement of the anode with the associated cathode, ignition means comprising a source of current connected with said cathodes operable responsive to failure of the flow of current through any one of said valves to supply current impulses to the solenoid of said one of said valves only and to connect said source with the ignition anode of said one of said valves only, and timing means responsive to initiation of the operation of said ignition means for rendering said ignition means inoperative after a predetermined time interval.

18. In a control system for a plurality of interconnected electric valves each comprising an ignition anode, excitation anode means, a cathode, and a solenoid for controlling the engagement of the ignition anode with the associated cathode, ignition means comprising a source of current connected with said cathodes operable responsive to failure of the flow of current through any one of said valves to supply current impulses to the solenoid of said one of said valves only and to connect said source with the ignition anode of said one of said valves only, excitation means comprising a source of current connected with said excitation anode means for supplying continuous excitation current to each of said cathodes to maintain said valves continuously conductive, and means for rendering said valves simultaneously non-conductive for! the flow of current between said circuits comprising timing means responsive to operation of said ignition means for rendering said ignition means and excitation means inoperative after a predetermined time interval.

19. The combination with an alternating current network, a direct current circuit, a pair of electric valves connecting opposite phases of said network with said direct current circuit and each comprising an anode, a control grid and a cathode, and excitation means for each of said valves, of means responsive to failure of the excitation means of one of said valves for impressing on the grid of only the other one of said valves a potential rendering the valve non-conductive.

20. The combination with a polyphase alternating current network comprising a plurality of pairs of opposite phase portions, a direct current circuit, a plurality of pairs of electric valves severally connecting said pairs of phase portions with said direct current circuit and each comprising an anode, a control grid and a cathode, and excitation means for each of said valves, of means responsive to failure of the excitation means of one of said valves for impressing a potential on the grid of only the valve forming a pair with said one of said valves rendering the valve non-conductive.

21. The combination with an alternating current network, a direct current circuit, a pair of electric valves connecting opposite phases of said network with said direct current circuit and each comp-rising an anode, a control grid and a cathode, and ignition and excitation means for each of said valves, of means responsive to failure of the excitation means of one of said valves for rendering effective the ignition means of said one of said valves only and for impressing a potential on the grid of the other one of said valves only to render the valve non-conductive.

22. The combination with an alternating current network, a direct current circuit, a pair of electric valves connecting opposite phases of said network with said direct current circuit and each comprising an anode, a control grid and a cathode, and ignition and excitation means for each of said valves, of means responsive to the flow of current through said excitation means operable upon failure of the excitation means of one of said valves for rendering efiective the ignition means of said one of said valves and for impressing a potential on the grid of the other one of said valves only to render the valve nonconductive until restoration of the operation of the excitation means of said one of said valves.

23. The combination with an alternating cur rent network, a direct current circuit, a pair of electric valves connecting opposite phases of said network with said direct current circuit and each comprising an anode, a control grid and a cathode, and ignition and excitation means for each of said valves, means for impressing on said grids potential controlling the conductivity of said valves, of means responsive to failure of the excitation means of one of said valves for rendering effective the ignition means of said one of said valves and for modifying the potential of the grid of the other one of said valves only to render the valve non-conductive.

SAMUEL R. DURAND. 

